PURPOSE

For example, a project might choose to have multiple streams of development
and use a different tag for each stream,
e.g., stable, beta, dev, canary.

By default, the latest tag is used by npm to identify the current version of
a package, and npm install <pkg> (without any @<version> or @<tag>
specifier) installs the latest tag. Typically, projects only use the latest
tag for stable release versions, and use other tags for unstable versions such
as prereleases.

The next tag is used by some projects to identify the upcoming version.

By default, other than latest, no tag has any special significance to npm
itself.

CAVEATS

This command used to be known as npm tag, which only created new tags, and so
had a different syntax.

Tags must share a namespace with version numbers, because they are specified in
the same slot: npm install <pkg>@<version> vs npm install <pkg>@<tag>.

Tags that can be interpreted as valid semver ranges will be rejected. For
example, v1.4 cannot be used as a tag, because it is interpreted by semver as
>=1.4.0 <1.5.0. See https://github.com/npm/npm/issues/6082.

The simplest way to avoid semver problems with tags is to use tags that do not
begin with a number or the letter v.